There are known methods and devices for controlling a capacitive element, in particular piezoelectric actuators for controlling fuel injection in an internal combustion engine.
The properties of the piezoelectric actuator depend on temperature. Therefore, the temperature of the piezoelectric actuator must be determined. In addition, there are deviations in the properties of piezoelectric actuators and controllers of the same design. An object of the present invention is to classify piezoelectric actuators and controllers.
In the case of such piezoelectric actuators, in particular when used in an internal combustion engine to control the amount of fuel injected, the situation may occur where the piezoelectric actuator is driven so that it remains in a certain position, e.g., in the case of a fuel control valve, in a position in which there is continuous fuel injection. Then if a change in the charge of the piezoelectric actuator is no longer possible due to a fault, the valve remains in this position with no change. Such safety-critical states are to be avoided with piezoelectric actuators.
Due to the fact that in the case of a controller having a capacitive element, an ohmic resistor is connected in parallel with the capacitive element, and the value (R) of the ohmic resistor is determined at certain times, and the type and/or temperature of the capacitive element is deduced on the basis of the value of the resistor, it is possible to determine the temperature easily and/or to compensate for the temperature dependence of the controller, to classify piezoelectric actuators and to reliably avoid critical operating states. This procedure is advantageous with all controllers having a capacitive element. It is especially advantageous with piezoelectric actuators.
It is especially advantageous if the value (R) of the ohmic resistor which is connected in parallel to the capacitive element is determined at certain times and then the temperature of the capacitive element and/or controller is deduced on the basis of this value.
It is especially advantageous that various objects can be achieved at the same time by means of this resistor.
It is advantageous if the value (R) of the ohmic resistor which is connected in parallel to the capacitive element is determined at certain times, and then the type and temperature of the capacitive element and/or controller are deduced on the basis of this value. In particular, the ohmic resistor is used both for classification and for temperature determination.
It is advantageous if the value (R) of the ohmic resistor which is connected in parallel to the capacitive element and functions as a discharge resistor is determined at certain times and then the type of capacitive element and/or controller is deduced on the basis of this value. In particular, the ohmic resistor is used both as a discharge resistor and for classification.
It is advantageous if the value (R) of the ohmic resistor which is connected in parallel to the capacitive element and functions as a discharge resistor is determined at certain times and then the temperature of the capacitive element and/or controller is deduced on the basis of this. In particular, the ohmic resistor is used both as a discharge resistor and for the determination of temperature.
Due to the fact that the ohmic resistor functions as a discharge resistor, controlled discharging of the capacitive element is possible. In particular, in the case when the controller is used as an injector for injecting fuel into an internal combustion engine, critical operating states can be avoided in this way.
This yields an especially simple method of calculating the value of the resistor due to the fact that resistance is calculated on the basis of a discharge time of the capacitive element. To do so, the capacitive element is charged to a voltage and then discharged across the ohmic resistor.
If the value of the resistor is determined on the basis of a test current and/or a test voltage, then the value can be corrected constantly in ongoing operation without any negative effect on the resistance of the controller.
It is especially advantageous if the value of the resistor is determined before starting operation of the controller for the first time.
Such an initial startup occurs at the end of the production line or after repair and/or replacement of the controller.